The present invention relates to a nonaqueous electrolyte and a lithium-ion secondary battery using the same.
In recent years, requirement for compact-sizing or making energy density higher has been increasing, as for a power source for mobile communication such as a mobile phone, or a mobile personal computer. In addition, development has also been progressing such as a storage power source of midnight power, or a power source for power storage in combination of a solar battery or wind-power generation. Commercial application has also been progressing of an electric car, a hybrid vehicle and a hybrid train utilizing electric power as a part of motive power.
As the nonaqueous electrolyte, the one in which an electrolyte such as lithium hexafluorophosphate is dissolved in a nonaqueous solvent such as ethylene carbonate has widely been known. Such a nonaqueous solvent is generally easy to volatile, and has inflammability. In particular, for application of a relatively large-size lithium secondary battery such as the power source of power storage, use of the nonaqueous electrolyte without fear of flashing has been desired.
Accordingly, research on furnishing flame retardancy to the non-aqueous electrolyte by blending a flame retardant agent has been promoted energetically.
In JP-A-2006-4746, there has been disclosed a nonaqueous electrolyte for a secondary battery, wherein a specified phosphorous compound is contained in extremely low concentration in the nonaqueous electrolyte. It has also been described the effect that durability at high temperature is improved and decrease in initial capacity suppression is suppressed significantly by this nonaqueous electrolyte.
In JP-A-2002-203598, there has been disclosed a nonaqueous electrolyte wherein a lithium salt is dissolved in a nonaqueous solvent having a flash point of equal to or higher than 70° C., containing a cyclic carboxylate ester and a carbonate ester, and still more a cyclic phosphoric acid ester and/or a chain phosphoric acid ester are added.